1. Field of the Invention
The invention relates to a circuit arrangement for testing the connection of a sound reproducing device to a sound signal source and in particular to such a circuit arrangement for use in a sound reproducing apparatus on board a vehicle, for example a car radio.
2. Description of the Related Art
With such connections between sound signal sources and sound reproducing devices the diagnosis of fault causes in the case of incorrect operation may be difficult depending on the construction. For example, a concealed mounting of such apparatuses may inhibit a rapid location of the fault sources. Particularly in the case of complex apparatuses with a large number of possible fault sources the diagnosis and repair of faults may prove to be very laborious.
It is an object of the invention to provide a circuit arrangement for testing the connection of a sound reproducing device to a sound signal source and enabling the condition of this connection to be determined simply and rapidly.
According to the invention this object is achieved by a circuit arrangement for testing the connection of a sound reproducing device to a sound signal source, to which sound signal source a supply voltage from a power supply can be applied via an impedance and to which the sound reproducing device is connected, the circuit arrangement comprising
a power control device for controlling the sound signal power to be supplied to the sound reproducing device by the sound signal source,
a voltage measurement device for measuring the supply voltage supplied by the power supply via the impedance in dependence on the sound signal power to which the sound signal source has been set, and
a comparison device for comparing the measured values of the supply voltage for two different given values of the sound signal power, and for producing a fault signal if the measured values of the supply voltage do not differ from one
another by a given amount.
The invention enables an effective diagnosis of faults in the connection of a sound reproducing device to a sound signal source without the use of any additional test means. Such a fault diagnosis can be effected very simply, for example without any test equipment, even by an unskilled user. Thus, this user can test the apparatus rapidly and accurately for given fault causes without recourse to, for example, services and personnel of a professional workshop. In such a case fault-finding is also simplified for skilled personnel, which altogether results in a substantial reduction of maintenance and repair costs.
The invention advantageously utilizes the recognition of the fact that the current drawn from the power supply by the sound signal source increases as the sound signal power increases and produces an increasing voltage across the impedance via which the supply voltage is applied from the power supply to the sound signal source. However, the current and the voltage produced by this current will not appear if the sound reproducing device is not connected to the sound signal source. Thus, interruptions of the connection between these two parts of the relevant apparatuses can be detected simply. Conversely, the power supply will have to furnish an excessive current in the case of a short-circuit in the connection between the sound reproducing device and the sound signal source, which also results in a voltage which deviates from the rated value. In this way, it is also possible to detect short-circuits or similar faults.
The relevant impedance need not be included separately in the connection from the power supply to the sound signal source. Preferably, the impedance is formed by a smoothing circuit for the supply voltage, which is present anyway, or a finite internal resistance, which is always available in the case of real power supplies.
According to the invention the circuit arrangement for testing the connection is adapted to perform a comparison measurement to eliminate fluctuations in absolute value of, for example, the voltage furnished by the power supply. Thus, a very fine and accurate detection of even small supply voltage variations is possible.
In an advantageous embodiment of the circuit arrangement in accordance with the invention the power control device, the voltage measurement device and the comparison device are parts of a control circuit for controlling the operation of the sound signal source. Preferably, this control is effected digitally by means of a microprocessor. This minimizes the complexity of the circuitry required for the invention.
In particular, the power control device may also be formed by a volume control included in the control circuit, so that this neither requires any additional circuitry. Testing is performed, for example, by an additional control program incorporated in the microprocessor. Thus, operational control of the normal operation of the sound reproducing device and the sound signal source and control of the test process can be effected by a common component.
In a further embodiment of the invention a device for producing a fault signal in the form of an acoustic signal may be provided, which device in particular comprises a buzzer device. Such a buzzer device, or a similar device for producing an acoustic signal, can produce a simple fault signal independently of the sound reproducing devices to be tested, i.e. also in the case that inadvertently these devices have not been connected. Another possibility of producing a fault signal is an optical indication, for example on a display device which is available anyway for the display of operating parameters of the sound signal source.
Another embodiment of the invention comprises a test sound source for applying a test wave to the sound signal source and, for the measurement of the supply voltage, the sound signal source is adapted to apply a sound signal based on the test wave and having a given sound signal power to the sound reproducing device. As compared with a test by a test signal to be generated by the sound signal source, for example, on the basis of a radio signal received via an antenna, this embodiment of the invention has the advantage that the test is performed on a well-defined basis because unpredictable fluctuations of the signals supplied by the sound signal source can be excluded. An advantageous simplification of the circuitry is obtained by an improved embodiment in that the device for producing the fault signal in the form of an acoustic signal includes the test sound source. This enables the test signal source to be used both for generating the test wave and for generating the fault signal.
In a further embodiment the sound reproducing device comprises at least one loudspeaker and the measurement of the supply voltage can be effected separately for each loudspeaker. This enables an effective testing of more extensive sound reproducing devices, particularly stereo systems in motor vehicles, to be carried out, because these often comprise a plurality of loudspeakers. Advantageously, the program controller for testing the individual loudspeakers is then coupled to the balance and/or fader controls.